Higher Ridgeway – Thermal Assessment
Higher Ridgeway September 2010
Gale & Snowden M&E
Gale & Snowden Ltd
Higher Ridgeway
Prepared by:
Jason Fitzsimmons
Checked by:
Rebecca Dawkins / Maria Gale
Version:
Draft 01
Job No:
B0907
Reference:
G&SOffice\Mechanical\B0907KevinMcCabe\Thermal & Solar Assessment
Rev No
Comments
Page 2 of 27
Date
This document has been produced by Gale & Snowden for the Higher Ridgeway scheme and is solely for the purpose of assessing thermal & solar heat loads for the main rooms in the main house. It may not be used by any person for any other purpose other than that specified without the express written permission of Gale & Snowden. Any liability arising out of use by a third party of this document for purposes not wholly connected with the above shall be the responsibility of that party who shall indemnify Gale & Snowden against all claims costs damages and losses arising out of such use
Gale & Snowden Ltd 18 Market Place Bideford Devon EX39 2DR T: 01237 474952 F: 01237 425449 www.ecodesign.co.uk Company No. 5632356 VAT Registration No. 655 9343 06
Gale & Snowden Ltd
Higher Ridgeway
Page 3 of 27
Executive Summary The main building of the proposed development Higher Ridgeway has been thermally assessed for summer time conditions. The dwelling has a risk of overheating due to the high levels of insulation and air tightness that is to be achieved with the design. Whilst this approach makes use of trapped heat in winter so that internal temperatures can be maintained during cold periods via solar gains and equipment gains, this trapped heat can be detrimental in warmer conditions resulting in overheating. As these good insulation standards result in heat not being able to escape through the fabric, the only alternative is ventilation. The results, thermal simulations and conclusions have found: •
Natural ventilation control is critical at reducing unwanted gains during summer periods
•
Night cooling is also critical as day time ventilation alone would not be sufficient at reducing internal temperatures
•
Night cooling has a higher impact on internal temperatures than the stack ventilation system
•
The stack stairwell appears to be limited in its contribution compared to other forms of ventilation control such as opening upper windows and night cooling. It does have more impact on upper floors than the lower ground floor
•
Provided a robust control of natural ventilation is adopted during the day and night, internal temperatures have found to be quite reasonable
Gale & Snowden Ltd
Higher Ridgeway
Page 4 of 27
Contents Executive Summary
3
Contents
4
1
Introduction
5
1.1
This report
5
2
Thermal Modelling Software Tool
6
2.1
Thermal Modelling Software Tools
6
2.2
Dynamic Thermal Simulation Heat Gain Methodology
6
3
Input Parameters
7
3.1
Weather Files – Design Summer Year
7
3.2
Infiltration & Ventilation
8
3.3
Window & Vent Opening Profiles and Strategies
8
3.4
Internal heat gains
8
3.5
The Role of Thermal Mass
9
3.6
Quantifying Overheating
9
4
Building Constructions
10
4.1
Building Fabric
10
5
Summertime Heat Gain – Outputs & Results
11
5.1
Simulation Control Parameters
11
5.2
Simulation 0 Outputs - No Natural Ventilation
12
5.3
Simulation 1 Outputs – Daytime Ventilation Only
14
5.4
Simulation 2 Outputs – Daytime Ventilation with Stack Ventilation
15
5.5
Simulation 3 Outputs – Daytime & Night Time Ventilation with No Stack Ventilation
18
5.6
Simulation 4 Outputs – Daytime & Night Time Ventilation with Stack Ventilation
21
5.7
Additional Simulation Analysis
22
6
Conclusions
26
6.1
Stack Ventilation
26
6.2
Window Openings
26
6.3
Night Cooling
27
6.4
Summary
27
Gale & Snowden Ltd
1
Higher Ridgeway
Page 5 of 27
Introduction 1.1 This report This report details the outputs and information obtained from the thermal modelling exercise carried out on the proposed new development Higher Ridgeway. The report is intended to provide details of likely summertime temperatures for a range of given scenarios in key rooms in the main dwelling. The completed report is intended to inform the client of how the modelling exercise was carried out and how the results were arrived to help inform the design. Detailed herein are the construction details that were analysed, internal heat gains, weather files utilised, software methodology and analysis, ventilation strategies, results and findings, and conclusions. The results of the various simulations detailed do not provide every simulation and analysis carried out as these would have been too numerous to include and would render the report meaningless to most readers. The number of different building and thermal scenarios that can be simulated is infinite, as any alteration whether it is a construction detail or to a window opening strategy day and night will produce different results each time. Thermal simulations and results shown therefore are those considered appropriate in line with industry best practise guidelines and the experience of the thermal assessor. Hence, results detailed are those that have been found to impart the most meaningful data for comparison and analysis purposes.
Gale & Snowden Ltd
2
Higher Ridgeway
Page 6 of 27
Thermal Modelling Software Tool 2.1 Thermal Modelling Software Tools The thermal modelling software tools utilised to assess the buildings thermal performance include: •
Model tool:
ModelIT Building Modeller
•
Thermal tool:
Apache Thermal Calculation and Simulation
•
Solar analysis tool:
Suncast Solar Shading Analysis
•
Wind & air movement tool: Macroflo: Multi-zone Air Movement
•
Lighting tool:
FlucsDL – daylighting analysis
SunCast – Is a powerful solar analysis tool that enables solar geometry studies for the given latitude and longitude to be performed all year round and which can be linked into the thermodynamic ventilation simulation. This enables one to maximise or minimise the effects of solar gains upon the building. MacroFlo – This simulates air flow driven by wind pressure and buoyancy forces on the building. Thermal Simulation – Combined with Macroflo and SunCast this software runs an all year round 24 hours a day simulation with real weather data. Studies can then be carried out on natural ventilation, infiltration, facade analysis and the effect on summer time overheating.
2.2 Dynamic Thermal Simulation Heat Gain Methodology The heat gain methodology allows for dynamic thermal simulation. The main features of this method are as follows: •
The method uses dynamic thermal simulation based on first-principles mathematical modeling of the heat transfer processes occurring within and around the building
•
The thermal simulation is coupled with natural ventilation simulation via the Macroflo programme
•
It takes into account casual and solar gains
•
It takes into account building orientation and the dynamic properties of the materials used such as the decrement factor
•
It utilises real time weather data derived from the MET office and the typical Design Summer Year is input.
•
The simulation is run for a complete year 24 hours a day
Gale & Snowden Ltd
3
Higher Ridgeway
Page 7 of 27
Input Parameters 3.1 Weather Files – Design Summer Year The thermal modelling tool and analysis utilises real time weather data derived from the MET office and the typical Design Summer Year is input. The Design Summer Year (DSY) consists of hourly data for twelve typical months, selected from approximately 20-year data sets (typically 1983-2004), and smoothed to provide a composite, but continuous, 1-year sequence of data. The DSY consists of an actual 1-year sequence of hourly data, selected from the 20-year data sets to represent a year with a hot summer. The selection is based on dry bulb temperatures during the period April–September. Modelling a proposed building design against the DSY enables the likely thermal performance and likelihood of summertime overheating to be assessed by simulation under typical weather conditions. The year selected is the mid-year of the upper quartile. This enables the proposed building design of Higher Ridgeway to simulate thermal performance during a year with a hot, but not extreme, summer. This data has been substantially enhanced compared to the Met Office data on which they are based. Short periods of missing data have been filled using procedures designed specifically for this purpose. The difficulty of obtaining consistent irradiation data means that global and diffuse irradiances have been generated from synoptic data (mainly sunshine duration and cloud cover) using computer models. The parameters included in the data sets are: •
dry bulb temperature (°C)
•
wet bulb temperature (°C)
•
atmospheric pressure (hPa)
•
global solar irradiation (W·h/m2)
•
diffuse solar irradiation (W·h/m2)
•
cloud cover (oktas)
•
wind speed (knots)
•
wind direction (degrees clockwise from North)
Design Summer Years (DSYs) have been made available for the purpose of thermal modelling for 14 locations across the UK. The closest available weather data files for Ottery St Mary is Plymouth and the DSY for this location has been used as part of this assessment.
Gale & Snowden Ltd
Higher Ridgeway
Page 8 of 27
Graph 1: Design Summer Year Temperature Profile – Plymouth
35 30
Temperature (°C)
25 20 15 10 5 0 -5 Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Jan
Date: Mon 01/Jan to Mon 31/Dec Dry-bulb temperature: (PlymouthDSY05.fwt)
3.2 Infiltration & Ventilation 3
2
An air permeability of 0.75 m / m h @ 50Pa has been set for a continuous infiltration load For the purpose of assessing summer loads the MVHR ventilation was not included for. This system will be providing the minimal air flow for fresh air requirements only which will typically be less than 0.3 air changes per hour. Comparing this to an opening window which can generate 3 air changes per hour and upwards it was considered the MVHR contribution would be minimal. Past experience of thermal modelling has also found the MVHR contribution at removing internal gains to be minimal.
3.3 Window & Vent Opening Profiles and Strategies Various window opening profiles were input into the thermal model in order to assess summer time temperatures under different scenarios. Table 2 in section 5.1 details the opening profiles for different simulation parameters. Overheating in dwellings can be controlled via a mixture of different ventilation strategies such as: •
Day time window opening ventilation – this can be enhanced by making best use of wind pressure differentials one side of the dwelling to the other and encouraging cross flow ventilation by opening internal doors.
•
Night cooling can be effective at reducing heat gains absorbed during the day
•
Making the best use of exposed thermal mass such as directed plastered cob walls
•
Making the best use of the stack effect implementing high level vents and opening upper floor windows
3.4 Internal heat gains 2
2
Due to the size of the dwelling a modest 3 W/m was applied. At 400 m (internal floor area) this equates to 400 x 3 = 1.2 kW across the dwelling 24 hours a day. Internal heat gains are generated by equipment such as televisions, cookers, washing machines, and people and in some properties can make significant
Gale & Snowden Ltd
Higher Ridgeway
Page 9 of 27
contribution to a dwelling’s yearly heat demand. A modest allowance has been included, in reality this load will fluctuate throughout the 24 hour cycle depending on equipment used and occupancy patterns in the different rooms. During certain periods, for example the kitchen, fluctuations are likely to be much greater than this.
3.5 The Role of Thermal Mass Thermal mass in buildings is the term used to describe the absorption of heat by the building fabric. Its value in controlling overheating arises from the heat capacity of the mass of the building structure being sufficient to absorb significant quantities of heat with only a small increase in its own temperature. Buildings having a more heavy weight construction such as those of brick and block construction or more traditionally cob and stone can provide a means for introducing mass as a summertime overheating control mechanism if required. The thermal modelling exercise assesses the impacts of the different proposed construction materials for their affect on internal comfort conditions. The effect of thermal mass is a result of three properties of the material together with the total exposed mass: the thermal capacity of the material, the thermal conductivity and the density. These properties combine to produce a property known as the admittance of the material and a high thermal mass (high admittance) material changes its temperature more slowly than the air temperature around it. For the cob wall construction the following parameters have been input: •
Conductivity – 0.5 W / (m.K)
•
Density – 1750 kg / m3
•
Specific Heat Capacity – 891 J / (kg.K)
3.6 Quantifying Overheating The building regulations and best practise guides are very limited when it comes to quantifying and defining overheating in dwellings. It can also be partly subjective as what one individual is willing to accept as upper limits in internal temperatures would be different for another. An indicator for offices is used by CIBSE (Chartered Institute of Building Services Engineers) which looks 0 at the number of hours the internal temperature exceeds 25 C for schools the temperature threshold is 0 0 28 C. For the purpose of this exercise it was decided to use the 25 C figure as this is what the Passivhaus Institute also uses for dwellings to ensure that the figure is not exceeded for more than 10% of the time during a given year.
Gale & Snowden Ltd
4
Higher Ridgeway
Page 10 of 27
Building Constructions 4.1 Building Fabric The following is a summary of the U values, which have been provided by the architect for the proposed scheme. Figures have been used in the thermal analysis calculations to determine the maximum heat output of the heating system. Whilst some of the material elements and thicknesses are still being determined the key component for heat loss determination is the final Uvalue.
Table 1: Building Thermal Envelope Construction Element
Roof
External Wall
External Wall Stone Plinth
Ground Floor
Triple Glazing Double Glazing
Summary of Materials
• • • • • • • • • • • • • • • • • • • • • •
150mm soil 50mm drainage layer Single ply membrane 200mm jablite EPS150 Timber decking 250x50 joists at 400mm centres with 115mm jablite premium 70 insulation between joists Service void 15mm plasterboard and skim 15mm lime render 50mm battens 200mm jablite premium 70 850mm cob wall 15 lime plaster 225mm Stone 75mm celotex 100mm celcon solar block 200mm jablite 70E 215mm celcon solar block 200mm jablite 70E 100mm celcon solar block Lime plaster Hardcore 200mm Jablite premium 70 DPM 100mm concrete slab Ceramic tiles Triple glazed unit Total shading coefficient 0.63
• •
Double glazed unit Total shading coefficient 0.73
• • • • • •
2
U-Value, W/m K
0.10
0.11
0.06
0.10
1.0 1.5
Gale & Snowden Ltd
5
Higher Ridgeway
Page 11 of 27
Summertime Heat Gain – Outputs & Results 5.1 Simulation Control Parameters The following graphs and tables provide temperature details of some of the rooms during summer periods with no natural ventilation control. The purpose here was first to determine the rooms with the highest temperature profiles so that the analysis could concentrate on these key areas rather than every room in the proposed property.
Table 2: Window and Vent Opening Profiles
Simulation
Opening Profile
Temperature Control
Operating Profile
0
All windows and doors closed
-
00:00 – 24:00
1
Day time vent only - external windows & doors open 20% free area & no stack vent
2
Day time vent only - external windows & doors open 20% free area with stack opening
3
Day and night time vent – external windows and doors open 20% no stack opening
4
Day and night time vent – external windows & doors open 20% free area & with stack opening
0
08:00-20:00
0
08:00-20:00
0
00:00 – 24:00
0
00:00 – 24:00
Internal air temp > 22 C
Internal air temp > 22 C Internal air temp > 22 C
Internal air temp > 22 C
Note: 1.
20% free area opening of windows and doors allows a nominal opening area, windows and doors would in reality be opened more than this during certain temperature conditions.
2.
All conservatories had openings of approximately 0.5 m at the main entrance facade and 0.5m on the main glazed facade
3.
The double heighted conservatory adjacent the kitchen and bedroom had openings at both floor levels 2 2 of 0.5 m at the main entrance facade and 0.5m on the main glazed facade
4.
The stack ventilator proposed above the stairwell had an initial free area allowance of 0.3 m
5.
Thermal overheating simulations were ran between the month of April to September
6.
Assumes lower ground floor doors are open to allow air flow up the stack stairwell. It is understood that building fire regulations requirement are for doors to be fire doors and to remain closed. Hence fire grilles/vents would be required. The free area of opening internal doors was allowed for in the simulations.
2
2
2
Gale & Snowden Ltd
Higher Ridgeway
Page 12 of 27
5.2 Simulation 0 Outputs - No Natural Ventilation Graph 2: Living Room Temperatures
38
36
34
Temperature (째C)
32
30
28
26
24
22
20 Apr
May
Jun
Jul
Aug
Sep
Oct
Date: Sun 01/Apr to Sun 30/Sep Air temperature: family room (scenario 11.aps)
Graph 3: Music Room Temperatures 36
34
32
Temperature (째C)
30
28
26
24
22
20 Apr
May
Jun
Jul
Date: Sun 01/Apr to Sun 30/Sep Air temperature: music room (scenario 11.aps)
Aug
Sep
Oct
Gale & Snowden Ltd
Higher Ridgeway
Page 13 of 27
Graph 4: Conservatory to Music Room Temperatures
45
40
Temperature (째C)
35
30
25
20
15 Apr
May
Jun
Jul
Aug
Sep
Oct
Date: Sun 01/Apr to Sun 30/Sep Air temperature: conservatory music room (scenario 11.aps)
This initial snapshot temperature analysis of the spaces without any natural ventilation control found that naturally, the spaces with the highest temperatures were the conservatory spaces, followed by the living room, family room, master bedroom, music room, kitchen and main bedroom. This was to be expected due to these areas being either in a more southerly orientation or having elevated glazed areas or being affected by high temperatures in the conservatories. It was interesting to note the difference between the rooms on the music room side such as the kitchen and music room against the rooms on the more southerly facade (living room, family room, master bedroom). The temperature profile when comparing graphs 3 and 4 shows that at their peak there is approximately 2 degree C difference, the southerly rooms naturally being hotter. However, the rooms such as the music room although not facing south are still picking up considerable temperature gain and it appears that this is the influence of the conservatory space and glazed areas. During the summer mornings these conservatory spaces are subject to considerable solar gain peaking at 2.2 kW during certain high summer periods for the music room conservatory alone.
Gale & Snowden Ltd
Higher Ridgeway
Page 14 of 27
5.3 Simulation 1 Outputs – Daytime Ventilation Only This is with windows opening and no night cooling and no stack ventilation. Graph 5: Living Room Temperatures 28
27
26
Temperature (°C)
25
24
23
22
21
20 Apr
May
Jun
Jul
Aug
Sep
Oct
Date: Sun 01/Apr to Sun 30/Sep Air temperature: living room (scenario 4.aps)
Graph 6: Music Room Temperatures 29
28
27
26
Temperature (°C)
25
24
23
22
21
20
19
18 Apr
May
Jun
Jul
Date: Sun 01/Apr to Sun 30/Sep Air temperature: music room (scenario 4.aps)
Aug
Sep
Oct
Gale & Snowden Ltd
Higher Ridgeway
Page 15 of 27
Graph 7: Conservatory to Music Room Temperatures
32
30
28
Temperature (°C)
26
24
22
20
18
16 Apr
May
Jun
Jul
Aug
Sep
Oct
Date: Sun 01/Apr to Sun 30/Sep Air temperature: conservatory music room (scenario 4.aps)
5.4 Simulation 2 Outputs – Daytime Ventilation with Stack Ventilation This is with both windows open and stack ventilation open and no night cooling. In the following graphs blue depicts the previous simulation 1 and red depicts simulation 2. Graph 8: Living Room Temperatures – simulation 1 against simulation 2 28
27
26
Temperature (°C)
25
24
23
22
21
20 Apr
May
Jun
Jul
Aug
Sep
Date: Sun 01/Apr to Sun 30/Sep Air temperature: living room (scenario 3.aps)
Air temperature: living room (scenario 4.aps)
Oct
Gale & Snowden Ltd
Higher Ridgeway
Page 16 of 27
Graph 9: Living Room Temperatures July – Simulation 1 against simulation 2 28
27
26
Temperature (°C)
25
24
23
22
21
20 05
06
07
08
09
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
Date: Thu 05/Jul to Tue 31/Jul Air temperature: living room (scenario 3.aps)
Air temperature: living room (scenario 4.aps)
Graph 10: Music Room Temperatures – Simulation 1 against simulation 2
29
28
27
26
Temperature (°C)
25
24 23
22
21
20
19
18 Apr
May
Jun
Jul
Aug
Sep
Date: Sun 01/Apr to Sun 30/Sep Air temperature: music room (scenario 3.aps)
Air temperature: music room (scenario 4.aps)
Oct
31
01
Gale & Snowden Ltd
Higher Ridgeway
Page 17 of 27
Graph 11: Music Room Temperatures July – Simulation 1 against simulation 2 29
28
27
26
Temperature (°C)
25
24
23
22
21
20
19
18 02
03
04
05
06
07
08
09
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
01
Date: Mon 02/Jul to Tue 31/Jul Air temperature: music room (scenario 3.aps)
Air temperature: music room (scenario 4.aps)
In the previous graphs that highlight the effect the stack has on day time ventilation it would appear from the graphs alone that whilst the stack has some affect, it does not appear to be that significant. As these graphs were quite limited in the information they relayed in actual figures, it was decided to investigate the 0 number of hours that the rooms exceeded 25 C was investigated.
0
Table 3: Number of hours temperatures exceeds 25 C – simulation 1 against scenario 2 Simulation
Location
No of hours air 0 temp > 25 C
1
Living room
183
2
Living room
106
1
Music Room
79
2
Music Room
84
It can be seen that on the first floor the range difference between simulations 1 & 2 (no stack and introducing the stack) for the living room is 77 hours where as on the lower ground floor the difference is only 5 hours. Upon further investigation it was found that in the other spaces within the dwelling the introduction of the stack during the day had more effect on the upper floors than the lower ground floors. This could be for the following reasons: •
The lower ground spaces are already using a method of stack ventilation via the opening windows on the upper floors. Whilst the windows could be considered as in flow paths for outside air, some of them will be out flow paths (such as when on opposing sides of the building) and some will be operating in a hybrid mixing mode whereby air is flowing in and out of the opening window at the same time.
•
Window vents often operate in a mixed flow pattern mode where air is entering as well - a mixed flow pattern mode.
Gale & Snowden Ltd
Higher Ridgeway
Page 18 of 27
•
Other forces such as wind pressure differences on the opposing sides of the building during certain favourable conditions are creating sufficient means to cross ventilate the spaces from one window opening on side of the building to a window opening on the other side of the building. I.e. entering on one side of the building and exiting on the other.
•
In conjunction with the organic form of the building – the curved corridor walls also promotes the effect of cross ventilation.
•
The simulations were ran with all internal doors open thus promoting cross ventilation more than stack ventilation.
•
The stack ventilation requires a larger ventilation opening at the top of the stack to provide greater effect. Relative to the window opening the stack vent free area is relatively small.
5.5 Simulation 3 Outputs – Daytime & Night Time Ventilation with No Stack Ventilation
Graph 12: Living Room Temperatures – Simulation 3
28
27
26
Temperature (°C)
25
24
23
22
21
20 Apr
May
Jun
Jul
Date: Sun 01/Apr to Sun 30/Sep Air temperature: living room (scenario 2.aps)
Aug
Sep
Oct
Gale & Snowden Ltd
Higher Ridgeway
Page 19 of 27
Graph 13: Living Room Temperatures – Simulation 1, 2 &3 for the month of July 28
27
26
Temperature (°C)
25
24
23
22
21
20 02
03
04
05
06
07
08
09
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
01
Date: Mon 02/Jul to Tue 31/Jul Air temperature: room (scenario 3.aps) Air temperature: living room (scenario 4.aps) Simulation 1 =living blue, simulation 2 = red, simulation 3 = green
Air temperature: living room (scenario 2.aps)
Graph 14: Music Room Temperatures – Simulation 1, 2 &3 for the month of July 29 28
27
26
Temperature (°C)
25
24 23
22
21
20
19
18 02
03
04
05
06
07
08
09
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
Date: Mon 02/Jul to Tue 31/Jul
Simulation 1 music = blue, 2 = red, simulation 3 = green Air temperature: roomsimulation (scenario 3.aps) Air temperature: music room (scenario 4.aps)
Air temperature: music room (scenario 2.aps)
01
Gale & Snowden Ltd
Higher Ridgeway
Page 20 of 27
It can be clearly seen from graphs 13 and 14 that the introduction of night cooling via opening windows is having a marked effect upon the temperatures within the space as much as 2 degrees C in some instances. In fact it can be seen that night cooling via opening windows is more effective at controlling summertime internal temperatures than the introduction of daytime stack ventilation. The question remains as to what effect does the stack have when opened at night.
Graph 15: Air Flows through typical window opening in the living room This is for simulation 3 and for the month of August 35
200
180
30
160 25 140
120
15
100
80
10
Volume flow (l/s)
Temperature (째C)
20
60 5 40 0
20
-5
0 01
02
03
04
05
06
07
08
09
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
01
Date: Wed 01/Aug to Fri 31/Aug Dry-bulb temperature: (PlymouthDSY05.fwt)
Volume flow in: (scenario 3.aps)
Volume flow out: (scenario 3.aps)
It can be seen where blue represents flow in and green represents flow out, that air distribution flow often reverses between the directions through an opening window. Red represents the external temperature conditions.
Gale & Snowden Ltd
Higher Ridgeway
Page 21 of 27
5.6 Simulation 4 Outputs – Daytime & Night Time Ventilation with Stack Ventilation Graph 16: Living Room Temperatures – Simulation 1, 2, 3 & 4 28
27
Temperature (°C)
26
25
24
23
22
21
20 02
03
04
05
06
07
08
09
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
01
Date: Mon 02/Jul to Tue 31/Jul Air temperature: living room (scenario 3.aps)
Air temperature: living room (scenario 4.aps)
Simulation = blue, simulation Air temperature: 1 living room (scenario 1.aps)
2 = red, simulation 3 = green, simulation 4 = yellow
Air temperature: living room (scenario 2.aps)
Graph 17: Music Room Temperatures – Simulation 1, 2, 3 & 4
29 28 27 26
Temperature (°C)
25 24 23 22 21 20 19 18 02
03
04
05
06
07
08
09
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
Date: Mon 02/Jul to Tue 31/Jul Air temperature: music room (scenario 3.aps) Air temperature: music room (scenario 1.aps)
Air temperature: music room (scenario 4.aps)
Air temperature: music room (scenario 2.aps)
01
Gale & Snowden Ltd
Higher Ridgeway
Page 22 of 27
It can be seen from graphs 16 and 17 that by providing a combination of day ventilation, night cooling and stack ventilation reasonable internal temperatures can be arrived at. Night cooling itself provides the most significant impact on internal day time temperatures. This is due to the thermal mass built into the model of the cob walls and its corresponding admittance factor. 0
Table 4: Number of hours temperatures exceeds 25 C – Simulation 1, 2, 3 & 4 Simulation
Location
No of hours air 0 temp > 25 C
1
Living room
183
2
Living room
106
3
Living room
44
4
Living room
38
1
Music Room
84
2
Music Room
79
3
Music Room
33
4
Music Room
32
5.7 Additional Simulation Analysis It was decided to run some additional simulations to investigate in more detail the stack effect, in particular its effect on moderating ground floor temperatures and also the impact that stack vent opening area had on internal temperatures.
Table 5: Additional Simulations - Window and Vent Opening Profiles Simulation
5
6
7
8
9
10
Opening Profile Day time vent only - external windows & doors open 20% free 2 area with stack opening 0.6 m As simulation 5 & closing windows st nd on 1 and 2 floor to see effect of 2 stack @ 0.6 m As simulation 6 closing windows st nd on 1 and 2 floor to see effect of 2 stack – and opening stack to 2 m As simulation 6 closing windows st nd on 1 and 2 floor to see effect of stack – and opening stack back to 2 0.3 m As simulation 8 and with night cooling Ground floor closed to the stack and day night cooling on this floor
Temperature Control
Operating Profile
0
08:00-20:00
0
08:00-20:00
0
08:00-20:00
0
08:00-20:00
0
00:00 – 24:00
0
00:00 – 24:00
Internal air temp > 22 C
Internal air temp > 22 C
Internal air temp > 22 C
Internal air temp > 22 C
Internal air temp > 22 C
Internal air temp > 22 C
Gale & Snowden Ltd
Higher Ridgeway
Page 23 of 27
Graph 18: Family Room Temperatures – simulation 5, 6, 7, 8, 9, 10 29
28
27
26
Temperature (°C)
25
24
23
22
21
20
19
18 Apr
May
Jun
Jul
Aug
Sep
Oct
Date: Sun 01/Apr to Sun 30/Sep Air temperature: family room (scenario 10.aps)
Air temperature: family room (scenario 9.aps)
Air temperature: family room (scenario 6.aps)
Air temperature: family room (scenario 5.aps)
Air temperature: family room (scenario 8.aps)
Air temperature: family room (scenario 7.aps)
Simulation 5 = light blue, simulation 6 = pink, simulation 7 = yellow, simulation 8 = blue, simulation 9 = red, simulation 10 = green
Graph 19: Family Room Temperatures July – simulation 5, 6, 7, 8, 9, 10 (in more detail) 29
28
27
26
Temperature (°C)
25
24
23
22
21
20
19
18 02
03
04
05
06
07
08
09
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
Date: Mon 02/Jul to Tue 31/Jul Air temperature: family room (scenario 10.aps)
Air temperature: family room (scenario 9.aps)
Air temperature: family room (scenario 6.aps)
Air temperature: family room (scenario 5.aps)
Air temperature: family room (scenario 8.aps)
Air temperature: family room (scenario 7.aps)
01
Gale & Snowden Ltd
Higher Ridgeway
Page 24 of 27
2
35
1600
30
1400
25
1200
20
1000
15
800
10
600
5
400
0
200
-5
Volume flow (l/s)
Temperature (째C)
Graph 20: Air flows through typical 0.3 m stack vent opening
0 01
02
03
04
05
06
07
08
09
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
01
Date: Wed 01/Aug to Fri 31/Aug Dry-bulb temperature: (PlymouthDSY05.fwt)
Volume flow in: (scenario 3.aps)
Volume flow out: (scenario 3.aps)
2
Graph 21: Air flows through typical 0.6 m stack vent opening
35
2800 2600
30
2400 2200
25 2000 1800 1600 15
1400 1200
10
1000 800
5 600 400
0
200 -5
0 01
02
03
04
05
06
07
08
09
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
Date: Wed 01/Aug to Fri 31/Aug Dry-bulb temperature: (PlymouthDSY05.fwt)
Volume flow in: (scenario 6.aps)
Volume flow out: (scenario 6.aps)
01
Volume flow (l/s)
Temperature (째C)
20
Gale & Snowden Ltd
Higher Ridgeway
Page 25 of 27
0
Table 6: Number of hours temperatures exceeds 25 C – Music Room / Family Room – Simulations 0 - 10 Simulation
Opening Profile
Location
All windows and doors closed
Music Room / Family Room
Day time vent only - external windows & doors open 20% free area & no stack vent
Music Room / Family Room
Day time vent only - external windows & doors open 20% free area with stack opening 2 0.3 m
Music Room / Family Room
Day and night time vent – external windows and doors open 20% no stack opening
Music Room / Family Room
4
Day and night time vent – external windows & doors open 20% free area & with 2 stack opening 0.3 m
Music Room / Family Room
5
Day time vent only - external windows & doors open 20% free area with stack opening 2 0.6 m
Music Room / Family Room
6
As simulation 5 & closing windows on 1st and 2nd floor to see effect of stack @ 0.6 2 m
Music Room / Family Room
7
As simulation 6 closing windows on 1st and 2nd floor to see effect of stack – and 2 opening stack to 2 m
Music Room / Family Room
8
As simulation 6 closing windows on 1st and 2nd floor to see effect of stack – and 2 opening stack back to 0.3 m
Music Room / Family Room
As simulation 8 and with night cooling
Music Room / Family Room
Ground floor closed to the stack and day night cooling on this floor. Windows open upstairs.
Music Room / Family Room
0
1
2
3
9
10
No of hours air 0 temp > 25 C 3367 / 3754
84 / 100
79 / 90
33 / 28
32 / 24
79 / 88
111 / 180
102 / 132
137 / 225
41 / 39
16 / 21
It is to be noted that closing upper floor windows and rooms is making these spaces warmer which will be adding temperature to the space below.
Gale & Snowden Ltd
6
Higher Ridgeway
Page 26 of 27
Conclusions 6.1 Stack Ventilation The effect of the stack and its vent opening (control and free area) can be seen in tables 4 and 6 and graphs 15 – 16. Reviewing simulations 1 – 4 it appears initially that the stack and its openings has little effect on reducing overheating in the lower ground floor room of the music room. With the stack closed the 0 number of hours where temperatures exceed 25 C in the music room is 33 hours, when the stack is open this is reduced to 32 hours, a difference of one hour. The stack appears to have greater effect in the upper ground floor living room where the difference is 4 hours, however even this is not that significant. Upon further analysis it was found that the stack worked more effectively when the windows on floors above were shut, thus suggesting that the upper floor windows which would have a larger opening area then the stack opening would be providing a path of lower resistance for the air to rise up and out of. It is important to note air is essentially a very light fluid and its fluid dynamics is very unpredictable and the following parameters would all have been having an effect on the results and temperature profiles. •
Air flow within buildings is due to pressure differences created by wind and the height of internal stack of air; also as a result of the difference between outside and inside temperatures
•
Air flow as with any fluid always follows the path of least resistance
•
Air can flow into an opening in one direction during certain conditions; it can also flow into and out of the same opening in a mixed mode manner during other certain conditions.
•
Air can typically flow in at low level and up and out of a stack when pressure and temperature conditions dictate. Equally it can also flow down a stack and out at low level during other favourable conditions (see graphs 15, 20 and 21).
•
Wind pressure is the main driving force in air movement within buildings followed by temperature. During hot still days this reverses and temperature difference between inside and outside is the main driving force. This is the advantage stack ventilation can have over other modes of natural ventilation such as cross flow from one side of the building to the other which relies predominately on wind pressure. Stack ventilation due to its height can provide means for hot air to rise up the stack providing the temperature differential between the higher and lower levels. However, if a temperature differential cannot be generated (i.e. when the internal temperatures are close to external temperatures) then there is little driving force on hot, still days. This is another reason why it is important to control summertime overheating. When the interior space is cooler than outside the stack reverses in operation and operates in downward flow mode.
Doubling the stack ventilation free area appeared to have little effect in reducing the number of hours over 0 25 C when comparing simulation 2 and simulation 5. It was then decided to close the upper windows on the upper ground and first floor to determine if this was affecting the results of the stack. Simulations 6, 7 and 8 show a marked difference between the different opening areas and the number of hours the spaces 0 exceed 25 C. This suggests that if windows are not opened sufficiently on the upper floors the stack vent will provide some benefits in reducing overheating. The main conclusion observed is that the stairwell (as it is centrally located within the dwelling) is already acting as a stack system between the floors when internal doors and external windows are opened.
6.2 Window Openings The control parameters input into the model such as the windows opening 20% free area when internal 0 conditions exceed 22 C are idealistic. In reality with manual control of windows there would not be this close level of control. Acceptable internal temperature and comfort levels are subjective and differ from person to person. Occupancy and energy patterns within dwellings compared to commercial buildings such as offices are also difficult to predict. Different dwellings can have different occupant lifestyles which
Gale & Snowden Ltd
Higher Ridgeway
Page 27 of 27
can change over time and from day to day. Offices on the other hand are predictable, occupied 5 days a week 9-5 hours – people, energy, and ventilation loads are easier to predict and input into a thermal assessment Hence in a dwelling windows could be opened sometimes when internal temperatures are lower sometimes higher, and the opening area of the window vents could also be greater or smaller than input into the simulation. During hotter periods it would be expected that window vents and doors would be fully opened when the dwelling is occupied. Due to these subjective control parameters it was decided to keep the opening input parameters simple and allow a reasonable estimate of how windows would be controlled.
6.3 Night Cooling It is very obvious from the various results such as from tables 4 and 6 that as well opening windows during the day the most significant impact on internal temperatures is the implementation of a night cooling strategy. Super insulated properties that minimise heat loss in winter by retaining heat can have a detrimental effect during summer periods. Night cooling in conjunction with the thermal mass of the building is far more effective than the stack at reducing internal temperatures. In the living room alone 0 comparing simulation 8 and simulation 9 (table 6) there is a 186 hour reduction in hours exceeding 25 C when night cooling is introduced. Simulation 10 provides results that show that if the ground floor is closed to stack ventilation due to fire restrictions and fire doors remain closed, day and night cooling via opening windows would be more beneficial than opening the ground floor to the stack.
6.4 Summary The results and conclusions herein do not detail every graph and every simulation that was ran for this scheme but provide a likely picture of the internal thermodynamics of the building. It points out likely temperature profiles and levels of overheating under different scenarios. Provided that there is good natural ventilation control during the day and that a night cooling strategy is adopted the building appears to be fairly robust. The results appear to show that the dynamics of window opening between floors and opposing sides of the building have more effect than the stack. The limitation of the stack will be its opening areas compared to window opening area. The results should not write the stack ventilation off automatically as it still has its part to play in providing a thermally robust building as it could add some additional control automatically over the manual control of windows. It will also help on the hot still days. The results will help in forming a cost benefit analysis when decisions are being made as to whether stack ventilation is worth implementing. One other key area concluded from this modelling exercise is: •
Conservatory areas would benefit from high and low level opening window vents and or opening window vents in the facade that does not contain the door. This will help with self venting when these spaces get too hot. During certain times of the year this will be beneficial to the building during others it will not.